Synthesis of Zeolite X from Waste Sandstone Cake Using Alkali Fusion Method

Transcription

1 Materials Transactions, Vol. 49, No. 3 (8) pp. 61 to 618 #8 The Japan Institute of Metals Synthesis of Zeolite X from Waste Sandstone Cake Using Alkali Fusion Method Takaaki Wajima 1; *, Kazuharu Yoshizuka, Takashi Hirai and Yasuyuki Ikegami 3 1 Department of Materials-process Engineering & Applied Chemistry for Environments, Akita University, Akita 18-85, Japan Department of Chemical Engineering, The University of Kitakyushu, Kitakyushu , Japan 3 Institute of Ocean Energy, Saga University, Imari , Japan During quarrying, waste stone cake is discharged as industrial waste. In this study, we attempted to convert waste sandstone cake to zeolitic materials using alkali fusion method. By varying the experimental conditions different types of the product were obtained, e.g. zeolite-x, zeolite- P, hydroxysodalite, tobermorite, and nepheline. The siliceous minerals in the cake were transformed into soluble phases, while calcite remains in the solid after 4-agitation following alkali fusion. The optimum condition of zeolite-x synthesis in the product is that the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C, and heating time at 8 C is less than 1 h. The results of the sorption experiments suggest that the product can be applied in environmental field such as the removal of pollutant. [doi:1.3/matertrans.mra75 (Received October, 7; Accepted December 17, 7; Published February 6, 8) Keywords: zeolite-x, waste sandstone cake, synthesis, alkali fusion, adsorption capacity 1. Introduction Effective use and recycling of resources are the important issues in the 1st century. During quarrying, waste stone cake is discharged as an industrial waste. The amount of the cake is 5 millions tons per year in Japan. Although a part of the waste is used as an artificial aggregate or some minor applications, a large part of it is dumped at landfills. In recent years, however, it is becoming more difficult to dispose of stone cake due to the lack of landfill sites. In Japan, furthermore, the Basic Law for Establishing a Recycling- Based Society and other laws to promote the effective use of resources are established, and improvement of recycling for construction waste materials and by-products is required. Since the stone cake is viewed as construction sludge, or waste, research and development has been conducted for its utilization in civil engineering as a foundation improvement or riverbed material. 1,) However, there have been no studies on its chemical conversion into functional materials. One of the effective utilization is to convert waste stone cake into zeolitic materials. Zeolites are a group of over 4 crystalline, hydrate alumino-silicate minerals with a structure based on a three-dimensional network of aluminum and silicon tetrahedra linked by sharing of oxygen atoms. Due to specific pore sizes and large surface areas, zeolites have the potential for a wide range of applications such as molecular sieves, adsorbents, and catalysts. 3) Many researchers reported the synthesis of zeolite from industrial wastes, e.g., coal fly ash, paper sludge ash, municipal incinerated ash, waste porcelain or perlite, which were mainly composed of SiO and Al O 3 in amorphous phases 4 1) with the different hydrothermal activation methods, such as classic alkali activation, 13) alkali fusion, 14) two-stage synthesis, 15) acidleaching, 16) and addition of silica sources. 17,18) One of the waste stone cakes, sandstone cake, mainly composed of quartz, feldspar, and calcite, having high *Corresponding author, wajima@gipc.akita-u.ac.jp content of SiO and Al O 3. However, since most of SiO and Al O 3 are in crystalline phases, it is difficult to dissolve into alkali solution by hydrothermal reaction. Shigemoto et al. 14) reported that less-active crystalline components, mullite and quartz, for zeolite formation by hydrothermal reaction could be converted into zeolite-x due to the change from crystalline components to soluble phases by alkali fusion. Zeolite-X (faujasite type) is high functional zeolite, which can be used as not only cation exchanger and adsorbent but also molecular sieves and a catalyst, and has been found widespread application in purification and separation of gases and organic components. Therefore, zeolite-x is one of the important targets for the zeolite synthesis from waste. In a previous study, the authors tried to convert the sandstone cake into zeolitic material by alkali fusion method, and succeeded to synthesize zeolitic material with high cation exchange capacity from the cake. 19) By alkali fusion, most of the crystalline phases could be converted into soluble phases, and transformed into zeolite crystals, zeolite-x and hydroxysodalite. This is a new way to convert the cake into functional materials. Little information is available, however, on pre-treatment of alkali fusion condition for synthesizing zeolitic materials from the cake. The elucidation of the reaction condition is the important issue for designing the manufacturing equipment and operation conditions. In this study, we attempted to convert the crystalline phases of the cake into soluble phases by alkali fusion followed by synthesizing zeolitic materials at low temperature (8 C). We determined the conditions of alkali fusion for a large amount of soluble phases to obtain high productivity of zeolite X. In addition, as one of the application of the obtained product, the properties of the obtained product for adsorption of NH þ 4 and Sr þ were investigated. NH þ 4 is usually the leading cause of eutrophication, and Sr þ is the most abundant radionuclides in nuclear fission products that are routinely or accidentally released. We focused on our attention on NH þ 4 and Sr þ removals from aqueous solutions simulating domestic and

2 Synthesis of Zeolite X from Waste Sandstone Cake Using Alkali Fusion Method 613 Intensity (cps) Fig. 1 Table 1 agro-industrial wastewater and radioactive wastewaters from nuclear power plants, respectively.. Materials and Methods Chemical composition of waste sandstone cake. Oxide (mass%) Waste sandstone cake SiO 38.9 Al O 3 1. CaO 6.9 Na O 1.4 K O 1.8 MgO.7 Fe O CO 3.6 SO 3.1 P O 5.1 Total : Quartz [SiO : Calcite [CaCO 3 : Albite [Na Al Si O 8 : Muscovite [KAl 3 Si 3 O 1 (OH) : Clinochlore [(Mg, Fe, Al) 6 (Si, Al) 4 O 1 (OH) θ [CuKα (degree) 6 Powder X-ray diffraction patterns of waste sandstone cake. 7.1 Raw materials The waste sandstone cake was obtained from one of the quarry in Kitakyushu, Fukuoka prefecture, Japan. Before the experiment, the cake was washed with distilled water and dried in an oven at 6 C overnight. The particle diameter is 3 mm in average. The chemical compositions of sandstone cake, determined by X-ray fluorescent spectrometry (XRF, ZSX11e, Rigaku), are listed in Table 1. Figure 1 shows the components of the waste stone cake determined by XRD (RIGAKU, XRD-DSC-XII). The cake is mainly composed of SiO and Al O 3 in the form of silicate and aluminosilicate minerals, such as quartz, albite, muscovite, and clinochlore. It also contained much CO thought to have originated in carbonate, mainly calcite.. Alkali fusion To investigate the relationship between the properties of fusion conditions and fused materials, the alkali fusion was carried out as follows. 1 g of the cake was mixed with 4, 8, 1, 16, and g of NaOH and grounded to obtain a homogeneous mixture. This was then heated in a nickel crucible in air at,,, and C for 1 h. The resultant fused mixture was cooled to room temperature and grounded again..5 g of each mixture was added to ml of distilled water in 1 ml tube made by polymethylpentene. Aging was carried out with vigorous agitation by reciprocal shaker at room temperature. After 4-h agitation, the solid product was filtered, washed with distilled water, and dried in the drying oven at 6 C overnight. The characterization of the solid phase was carried by XRD. To determine the solubility of Si, Al, and Ca from the solid obtained in each condition,.1 g of the solid was added to 1 ml of 1 M HCl solution, and shaken for 6 h. This mixture was filtered, and the concentrations of Si, Al, and Ca in the filtrate were determined by ICP-AES (Shimadzu, ICPS-75), to calculate the solubility of the solid..3 Zeolite synthesis after fusion To synthesize zeolitic phases from the solid obtained in each fusion condition, the slurry after agitation was heated at 8 C for 3, 6, 1, 4, and 48 h in water bath. The solid product was filtered, washed with distilled water, and dried in a drying oven at 6 C overnight. The phases of the product were analyzed by XRD, and the morphologies of the product were observed by scanning electron microscope (SEM) (TOPCOM, SM-)..4 Adsorption of NH þ 4 and Sr þ The adsorption properties of NH þ 4 and Sr þ on the products were investigated using 3 samples: (1) raw sandstone cake, () the product, (3) commercial zeolite-13x (Wako). The product was synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C). The aqueous solution of each.8 mm of NH þ 4 and 1.4 mm of Sr þ prepared with NH 4 Cl and SrCl, respectively..1 g of sample was added to ml of each aqueous solution. During stirring, ph was kept to neutral (6. 8.). A aliquot of ml suspension was removed at various time and filtered. The concentration of NH þ 4 in the filtrate was determined by the method of Koyama et al., ) and the concentration of Sr þ by ICP-AES. The corresponding adsorption amounts (q) were determined from the material balance as follows. q ¼ ðc CÞL w where C and C are initial and measured concentrations of NH þ 4 or Sr þ in the filtrate (mmol/l), L is volume of aqueous solution (L), and w is weight of the sample (g). 3. Results and Discussion 3.1 Alkali fusion The results of the fusion experiment are listed in Table. The first column of the table shows the mixed ratio of NaOH to the cake, and the second column indicates the fusion temperature. The columns from third to fifth show the soluble contents of the solid after 4-h agitation following the alkali

3 614 T. Wajima, K. Yoshizuka, T. Hirai and Y. Ikegami Table Soluble contents and mineral phases of fused material on various fusion conditions. Fusion condition Soluble contents (mmol/g) Mineral phases Temperature ( C) Si Al Ca Waste sandstone cake Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cal Qtz, Ab, Cal Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cal Cal Qtz, Ab, Cli, Ms, Cal Qtz, Ab, Cal Qtz, Ab, Cal Cal Qtz, Ab, Cal Cal Cal Cal Qtz, Ab, Cal Cal Cal Cal Qtz: Quartz, Ab: Albite, Cli: Clinochlore, Ms: Muscovite, Cal: Calcite Table 3 The product phases on various conditions. Fusion condition Synthesis time (h) Temperature ( C) 3 h 6 h 1 h 4 h 48 h.4 HS HS HS HS HS HS HS Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne.8 HS HS HS HS HS, P HS, P HS, P HS, P HS HS HS 1. X X, HS X, HS HS, To HS, To HS HS HS, To HS, To HS, To HS, To HS, To HS, To HS, P HS, P HS, To 1.6 X X, HS X, HS HS, To HS, To X, HS, P X, HS, P X, HS, P, To HS, To HS, To X, HS, P X, HS, P X, HS, P HS, To HS, To X X, P X, HS, P X, HS, P, To HS, To X, HS HS HS HS, To HS, To HS HS HS HS, To HS, To X, HS X, HS, P HS, To HS HS P P HS HS HS X: Zeolite-X, P: Zeolite-P, HS: Hydroxysodalite, To: Tobermorite, Ne: Nepheline fusion, and the sixth column indicates the remaining phases in the solid. All solids contain higher contents of soluble Si and Al than the raw cake, and soluble Ca contenting in all solids are almost same as the raw cake. The remaining mineral phases are divided into three patterns. Pattern I is that all five minerals in raw cake (quartz, albite, clinochlore, muscovite, and calcite) remained in the solid, pattern II is that minor two phases (chinochlore and muscovite) diminished and three minerals (quartz, albite, calcite) remained, and pattern III is that all silicate minerals (quartz, albite, clinochlore, muscovite) diminished and only calcite remained.

4 Synthesis of Zeolite X from Waste Sandstone Cake Using Alkali Fusion Method Pattern I + Ms+Cal Pattern II Qtz+ Ab+ Cal Qtz+ Ab+ Cli Pattern III Cal *Qtz: Quartz, Ab: Albite, Cli: Clinochlore, Ms: Muscovite, Cal: Calcite Fig. Remaining mineral phases in the solid after 4-h agitation following alkali fusion. The abscissa is the mixed ratio of NaOH to the cake, and the ordinate is the fusion temperature. To determine the relation between the soluble contents and mineral phases, the results are listed in Table. Figure and 3 also show the remaining phases and the amount of soluble Si, Al, and Ca in the solid after 4-h agitation following the alkali fusion, respectively. The abscissa is the mixed ratio of NaOH to the cake, and the ordinate is fusion temperature. In Fig. 3, black zone indicates the high solubilities of each element, and white means no soluble contents. With increasing the ratio of NaOH to the cake and fusion temperature (from bottom-left to top-right), as indicated by the arrow direction, the number of siliceous phases decreases (pattern I! pattern II! pattern III), the amounts of soluble Si and Al in the solid increased, and that of Ca is constant on all condition. The increases in soluble Si and Al are due to the decrease of siliceous minerals, which means that crystalline siliceous minerals are transformed into soluble phases by alkali fusion. The almost soluble Ca is originated from calcite on all fusion conditions, and calcite remains in the solid after fusion. From the results of Fig. and 3, the optimum conditions to transform the most contents of Si and Al in the cake into soluble phases is that the mixed ratio of NaOH to the cake is more than 1.6 and fusion temperature is higher than C. 3. Zeolite synthesis Table 3 shows the product phases on each fusion condition. Zeolite-X, zeolite-p, hydroxysodalite, tobermorite, and nepheline were obtained using the fusion method. In the case of low ratio of NaOH (< :8) at high temperature (> C), only nepheline was synthesized regardless of reaction time. That is, zeolite-x was synthesized before 1 h- reaction time, and then diminished. Alternatively, hydroxysodalite and tobermorite were frequently identified after 1 h-reaction time. Since zeolite-x was metastable phase, zeolite-x was easily transformed into hydroxysodalite and tobermorite after 1 h-reaction. Therefore, the synthesis for short period is important to obtain zeolite-x phases. Figure 4 shows the intensity of zeolite X in the product after the reaction time of (a) 3, (b) 6, and (c) 1 h. Black zone indicates the high intensity of zeolite-x, and white means no (a) Si (b) Al (c) Ca Fig. 3 Soluble contents of (a) Si, (b) Al, and (c) Ca in the solid after 4-h agitation following alkali fusion. The abscissa is the mixed ratio of NaOH to the cake, and the ordinate is the fusion temperature. zeolite-x. Regardless of synthesis time, the high intensity of zeolite-x was obtained at around 1.6 of the ratio of NaOH to the cake, and can be obtain at more than C even when the synthesis time is 1 h. Therefore, the best procedure is that the cake was fused with NaOH (the ratio of NaOH to the cake = 1.6) at more than C, and then heated at 8 C for less than 1 hours. Figure 5 shows the SEM photographs of (a) sandstone cake and (b) the product synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C). Although the raw materials are the fragments of rock shown in Fig. 5(a), octahedral crystals can be observed in the product, as shown in Fig. 5(b). Zeolite-X crystallizes in a typical octahedral form, and is a member of the faujasite

5 616 T. Wajima, K. Yoshizuka, T. Hirai and Y. Ikegami (a) 3 h (a) (b) 6 h (c) 1 h (b) Fig. 5 Scanning electron photomicrographs of (a) waste sandstone cake and (b) the product. The product was synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C) Fig. 4 Intensity of zeolite-x in the product after the reaction time of (a) 3 h, (b) 6 h, and (c) 1 h. The abscissa is the mixed ratio of NaOH to the cake, and the ordinate is the fusion temperature. group. Its structural framework comprises 4- and 8-membered rings. Figure 6 shows the X-ray diffraction patterns of (a) commercial zeolite-13x and (b) the product synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C). The obtained product was the mixture of zeolite-x and hydroxysodalite, and the intensity of zeolite-x in the product was approximately % of the commercial zeolite-13x. Since zeolite-x has high cation exchange capacity (5. mmol/g) and is a value-added material utilized as a molecular sieves or catalysts while hydroxysodalite has low cation exchange capacity (.3 mmol/g) and is low value-added material, the optimization of the synthesis conditions to produce only zeolite-x is necessary. In addition, the waste solution after zeolite synthesis is alkali solution with high Si content (approximately mg/l). We reported that zeolitic material was synthesized from powdered waste porcelain to discharge the alkali waste solution with high Si content and then the synthesis of pure zeolites from the waste solution with addition of Al sources. 1) By the same procedure, it would be possible to synthesize high-purity zeolite by addition of Al sources to the waste solution. 3.3 Removal of NH þ 4 and Sr þ We investigated the adsorption of the product, which was synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C), for NH þ 4 and Sr þ, to compare with those of raw cake and the commercial zeolite-13x. Figure 7 shows the adsorption abilities of (a) waste sandstone cake, (b) the product, and (c) the commercial zeolite-13x during the reaction. Although raw cake has no adsorption abilities for both NH þ 4 and Sr þ, the product has the adsorption abilities for both elements. The adsorption amounts of NH þ 4 and Sr þ on the product for are.5 mmol/g and 1. mmol/g, respectively, which are ca. 4% of those of the commercial material, because the product is the

6 Synthesis of Zeolite X from Waste Sandstone Cake Using Alkali Fusion Method 617 (a) : Zeolite-X (a) 3 Waste sandstone cake The product Commercial zeolite-13x Intensity (a. u.) q NH4+ (mmol/g) 1 (b) : Hydroxysodalite Reaction time, t / min θ [CuKα (degree) 6 Fig. 6 X-ray diffraction patterns of (a) commercial zeolite-13x and (b) the product synthesized at 8 C for 6 hours from the fusion material (fusion condition: the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C). (b) q Sr (mmol/g) Waste sandstone cake The product Commercial zeolite-13x mixture of zeolite-x and hydroxysodalite, and the amount of zeolite-x phase in the product is low, as shown in Fig. 6. The saturation time for NH 4 þ is min and that for Sr þ is 6 min, which is almost same as commercial material. This suggests that the adsorption ability mostly depends on zeolite-x phases in the product. The current product may be applied for water purification. By improving the synthesis process, higher content of zeolite-x in the product can be obtained, higher adsorption ability are expected lather than the current product. 4. Conclusions Zeolitic material can be synthesized from waste sandstone cake using the alkali fusion method. The siliceous minerals in the cake were converted into soluble material by alkali fusion, and zeolite-x, zeolite-p, hydroxysodalite, tobermorite, and nepheline were obtained. The best fusion conditions for the synthesis of zeolite-x are that the mixed ratio of NaOH to the cake is 1.6, fusion temperature is C, and heating time is 8 C for less than 1 h. The product has adsorption abilities of NH 4 þ and Sr þ, which are 4% of commercial zeolite-13x, and can be applied to water purification as a example. With improving the synthesis processes and conditions combination with acid-leaching, solvent extraction etc., we expect that the fusion method is promising as a new means of effective utilize waste stone to obtain highly functional products such as zeolite-x. Acknowledgments The analyses of the samples were carried out with XRD and XRF at the Instrumentation Center, The University of Kitakyushu. The work is supported by Grant-in-Aids for 1st Century COE Program and for Scientific Research (c), No from MEXT, and Salt Science Research Foundation, No. 51. REFERENCES Reaction time, t / min Fig. 7 The adsorption abilities of waste sandstone cake, the product and commercial zeolite-13x for (a) NH þ 4 and (b) Sr þ as a function of reaction time. Initial concentrations of NH þ 4 and Sr þ in the solution are.8 and 1.4 mm, respectively. 1) K. Nishida, T. Nishigata, Y. Tatsuta and T. Okumura: Proc. the 37th conf. Jpn. Geotech. Soc. (Japan Geotech. Soc., ) pp ) H. Tanaka: Inorganic Mater. 4 (1997) ) R. M. Barrer: Zeolites and Clay Minerals as Sorbents and Molecular Sieves, (Academic Press, London, 1978) pp. 1. 4) R. M. Barrer, R. Beaumont and C. Colella: J. Chem. Soc. Dalton Trans. (1974) ) R. Ruiz, C. Banco, C. Pesquera, F. Gonzalez, I. Benito and J. L. Lopez: Appl. Clay Sci. 1 (1977) ) A. Baccouche, E. Srasra and M. E. Maaoui: Appl. Clay Sci. 13 (1998) ) A. F. Gualtieri: Phys. Chem. Miner. 8 (1) ) D. Boukadir, N. Bettahar and Z. Derriche: Annual de Chimie Science des Materiaux 7 () 1 13.

7 618 T. Wajima, K. Yoshizuka, T. Hirai and Y. Ikegami 9) X. Querol, N. Moreno, J. C. Umaña, A. Alastuey and E. Hernández: Int. J. Coal Geol. 5 () ) G. C. C. Yang and T.-Y. Yang: J. Hazard. Mater. 6 (1998) ) T. Wajima and Y. Ikegami: Ars Separatoria Acta 4 (6) ) T. Wajima, H. Ishimoto, K. Kuzawa, K. Ito, O. Tamada, M. E. Gunter and J. F. Rakovan: Am. Miner. 9 (7) ) X. Querol, J. C. Umaña, F. Plana, A. Alastuey, A. López-Solar, A. Medinaceli, A. Valero, M. J. Domingo and E. Gracia-Rojo: Fuel 8 (1) ) N. Sigemoto, H. Hayashi and K. Miyamura: J. Mater. Sci. 8 (1993) ) G. G. Hollman, G. Steenbruggen and M. Janssen-Jurkovicova: Fuel 78 (1999) ) T. Wajima, K. Kuzawa, H. Ishimoto, O. Tamada and T. Nishiyama: Am. Miner. 89 (4) ) T. Wajima, M. Haga, K. Kuzawa, H. Ishimoto, O. Tamada, K. Ito, T. Nishiyama, R. T. Downs and J. F. Rakovan: J. Hazard. Mater. B13 (6) ) T. Wajima, T. Shimizu and Y. Ikegami: J. Environ. Sci. Health-A 4 (7) ) T. Wajima, K. Yoshizuka and Y. Ikegami: J. Jpn Soc. Eng. Geol. 47 (6) ) M. Koyama, T. Hori and Y. Kitayama: IARC Rep., Kyoto Univ. (1976) ) T. Wajima and Y. Ikegami: Ceram. Int. 33 (7)